Project Summary According to the National Institutes of Health, wound care costs approximately 25 billion dollars annually. Wound repair defects often occur in the skin of patients with diabetes, pressure ulcers, prolonged immobilization, and venous insufficiency. If a wound recurs, it almost exclusively recurs in the same location as the initial wound, due to the fragility of the fibrotic scarring that repaired the initial wound. Wound repair typically results in a region of fibrotic scar tissue. Contrastingly, skin regeneration fully recapitulates embryogenesis, completely restoring tissue function and adnexa, such as hair follicles. By understanding this process, we will be able to promote regeneration, thereby augmenting wound repair. This would reduce wound related hospitalizations and their corresponding medical costs, while also improving the quality of life for patients. To investigate skin regeneration, this proposal will use the Wound Induced Hair Neogenesis (WIHN) assay. For the assay, large full-thickness dorsal wounds are made on mice, and allowed to heal by contraction and re-epithelialization. In the center of these healed wounds, a variable number of hair follicles are fully regenerated and can be visualized non-invasively by confocal scanning laser microscopy (CSLM). After wounding, innate immune cells, primarily neutrophils and macrophages, are recruited to the wound bed to prevent infection and facilitate repair. The goal of this grant is to define the role of these cells in the regeneration process, focusing on their contribution to de novo hair follicle formation during WIHN. In Aim 1 we will investigate the hypothesis that small nuclear RNA expression and localization coincides with infiltrating immune cells. In Aim 2 we will investigate the hypothesis that infiltrating immune cells are required for WIHN. In Aim 3 we will investigate the hypothesis that immune cell extracellular traps promote hair follicle regeneration. These findings have the potential to lead to significant advances in the treatment of fibrotic diseases, affecting tissues such as skin, liver, and lung. This proposal is a mentored training grant that combines research efforts with a didactic plan necessary for the future transition of the PI to an independent position.